Prefoaming method for expanding particulate foamable material



March 18, 1969 D. E. STEVENS ETAL PREFOAMING METHOD FOR EXPANDINGPARTICULATE FOAMABLE MATERIAL Original Filed March 5, 1965 Sheet 4 of3INVENTQR5 fan/9E0 H. 00 V45 pa 540 1. .STC'l/EA/j BY m, m, M E E ATTOENEYS March 1969 D. E. STEVENS ETAL 3,432,937

PREFOAMING METHOD FOR EXPANDING PARTICULATE FOAMABLE MATERIAL OriginalFiled March 5, 1965 Sheet g ofS INVENTOR5 Eon/Hep H. D0 V45 DOA/Q4 0 1STEVE/v5 Mamh 1969 D. E. STEVENS ETAL 3,432,937

PREFOAMING METHOD FOR EXPANDING PARTICULATE FOAMABLE MATERIAL Sheet 3 of5 Original Filed March 5, 1965 INV ENTQR S Eowmeo H. Dos 4.5 {Do/v4.40E. 57-5412,

MM, M, M m

tates 3 Claims ABSTRACT OF THE DISCLOSURE :Work particles are exposed tolive steam substantially at atmospheric pressure, condensation beingprevented by otherwise heating the steam and the work by radiant heat toa temperature materially in excess of 212 F., the prefoamed particlesbeing delivered from such treatment substantially dry.

Background of invention The instant application is a division of myapplication Ser. No. 437,364, filed Mar. 5, 1965, now abandoned, andentitled Prefoaming of Expandable Synthetic Resin Such as StyrenePolymer Composition Containing a Volatile Organic Liquid.

Summary of invention For our particular purposes, the inventioncontemplates that the foamable resin will desirably be in the form ofpellets of a size comparable to sugar or salt. These will bedistributed, preferably in a thin layer, upon a screen belt which, inour practice, is a 40 x 40* mesh stainless steel belt. On this belt, theparticulate foamable material advances through a chamber in which it issubjected both to wet and'dry heat to effect prefoaming or partialexpansion of the individual particles. Live steam is desirable toinitiate the prefoaming but, in the open hood shown, it condenses at 212F.

The temperature to which the particles of expandable material should beexposed is critical, being in the neighborhood of 240 F. It is highenough so that there is considerable condensation if live steam alone isrelied upon to achieve any comparable temperature. Previous equipmentfor prefoaming has delivered the prefoamed material sufiiciently wet sothat up to twenty-four hours of drying time in an aerated bin has beenrequired, followed by de-clumping treatment.

In the instant device, condensation is virtually eliminated and a muchmore uniform temperature maintained by providing two sets of heatersbeneath the belt, one heater providing continuous dry heat forsubstantially the whole length of the chamber and other heaters beingarranged in sequence for delivering live steam beneath the belt orbeneath selected portions of the belt, the usual arrangement being suchthat the belt and the pellets to be prefoamed are exposed to live steamonly during their initial travel through the chamber and to additionaldry heat not only in the initial section but throughout the chamber. Theradiant dry heat maintains the temperature in the hood far above thecondensation point and the vapor is carried olf without wetting the Workbeyond the capacity of the terminal heater to deliver the work dry orsubstantially so, all vapor being carried away as rapidly ascondensation forms so that the pellets issue substantially dry.

As a result of these features, the prefoamed pellets are produced withan increased degree of uniformity and at a rate which is approximatelythree times the rate of production in the best competitve equipment.

atent The partially expanded material is delivered from the chamber ontoa vibratory screen which breaks any slight adhesion between particlesand discharges the prefoamed particles in relatively dry condition intoa pneumatic convection system by which they are conveyed to the point ofstorage or use.

The invention has both method and apparatus aspects.

Brief description 0 the drawings FIG. 1 is a view partially in sideelevation and partially in longitudinal section through equipment forpracticing the invention, parts being broken away.

FIG. 2 is a plan view taken on line 2-2 of FIG. 1 of the pan whichprovides the bottom portion of the heating chamber, portions of the beltbeing superimposed thereon and parts of the heating elements beingbroken away.

FIG. 3 is an enlarged view taken in cross section on the line 3-3 ofFIG. 1.

FIG. 4 is a fragmentary detail view taken in the plane indicated at 44in FIG. 3.

FIG. 5 is a fragmentary detail view taken in section on the line 55 ofFIG. 4.

FIG. 6 is an enlarged fragmentary detail view showing in plan apreferred form of conveyor belt.

FIG. 7 is a detail view taken in section on line 77 of FIG. 6.

FIG. 8 is a view partially in side elevation showing a modifiedprefoaming device, parts being broken away.

FIG. 9 is a greatly enlarged detail view taken in transverse sectionthrough a distributing screen covered drum which is a part of theapparatus shown in FIG. 8.

FIG. 10 is a view taken in section on line 1010 of FIG. 9.

Detailed description It will be understood that details given herein aresupplied to exemplify the best means known to us for practicing theinvention. They are given by way of example and not by way oflimitation.

In the preferred construction shown in FIGS. 1 to 7, the particulatefoama'ble material is delivered in any desired manner, as by pipe 12into a hopper 14 from which it issues into a vibrating pan 16 which isclosed at its rear margin 18 and reciprocated by a vibrating motor 20 todischarge the particles of material down the chute 22 onto the belt 24.The pellets may be placed on the belt to any desired depth, but tominimize adhesion of pellets to each other and to promote uniformity ofexposure to heat it is preferred to spread the pellets on the belt in asingle layer. The material as supplied to the machine appears likecoarse sugar or salt.

A belt 24 which has been used successfully is 40 x 40 mesh stainlesssteel screen cloth. The pan 26 in which the heating equipment is housedis spanned by an expanded metal web 28 which provides a foraminoussupport across which the work supporting run of belt 24 moves betweenthe pulleys 30 and 32. The pulley 32 is driven by a chain 34 throughspeed reducers 36 and 38 from motor 40.

We have found that the screen cloth belt 24 will not run true withoutspecial guide means for which a separate application is being filed butwhich will briefly 'be described herein. As best shown in FIGS. 2, 6 and7, bands 42 and 44 are connected to the sides of belt 24. In practice,these bands are made of polyethylene fixed to the belt by spaced rows ofstitching at 46. Beside each polyethylene band runs a link chain 48.Certain of the links are provided with laterally projecting arms at 50to which the respective bands are connected as 'by bolts 52. As bestshown in FIG. 7, the bands are preferably strengthened by being foldedupon themselves and the 3 margins stitched to 111C belt are reverselyfolded again at 54 so that the stitching 46 goes through four plies ofeach such band, with the margin of belt 24 centered between these plies.

The chains 48 ride on the out-turned margins 58 of pan 26 and are thusoutside of the treatment zone. This is best shown in FIG. 3 wherein thehood 60 is illustrated in cross section. This hood has lower marginalflanges turned outwardly at 62 and downwardly at 64 to engage flanges 58outside of the path of the chains 48. Thus, each chain operates in arecess offset from the feeding chamber and the bottom of which is theflange 58 of pan 26. Preferably, flexible aprons 66 of natural onsynthetic rubber are attached to the hood 60 and have their lowermargins closely proximate the screen cloth conveyor belt 24 to segregatethe work supporting areas of the belt from the side margins thereofwhich are fastened to the chains. It will be understood that chainsprockets 68 are provided coaxially with the belt guide pulleys and 32.

The hood progressively increases in height above the belt as clearlyshown in FIG. 1. Removable section 70 thereof is joined to a relativelyfixed section 72 which leads to the inlet 74 of a casing with which thevent pipe 76 communicates to carry off all vapor from the hood asrapidly as vapor is formed by condensation of the steam. The fact thatthe section 70 is removable facilitates access to the screen clothconveyor belt for cleaning or other purposes.

Within the pan 26 heating means is provided for delivering both steamand dry heat to work transported on the conveyor belt 24. The live steammay be provided by plural heater sections although only one is normallyused. The sections have separate supply lines 78 and 80 with separatevalves 82, 84 as shown in FIG. 2. Each section comprises a header 86from which perforated steam discharge pipes 88 lead longitudinall of pan26 beneath inverted channels 90. These channels are entirely open alongtheir lower margins and serve to distribute the steam substantiallyuniformly throughout the cross section of the pan 26. The steam passesupwardly through the expanded metal support 28 and the superimposedportions of the mesh conveyor belt 24 to act on the particulate workwhich is being transported through the treat ment chamber beneath hood60 On the surface of the belt.

Between the steam pipes 88 and the work are to and fro convolutions 92and 94 of steam pipes 96 and 98 which, for convenience, are arranged inparallel as best shown in FIG. 2 and are continuous from their inputends at the right of FIG. 2 to their discharge ends at the left of FIG.2. These exemplify any desired dry heating means, whether electrical orsteam or hot water, from which steam does not escape. It is found thatthe continuous dry heat provided by the element or elements 92, 94maintains a desirably higher temperature about the work than would beprovided by live steam alone and it also minimizes condensation eitheron the work or on the belt. In addition, the progressively increasingcross section of hood 60 and the association thereof with vent pipe 76results in isolating above the work the level at which condensationoccurs and withdraws the condensate vapor as fast as it condenses.

It is found that in practice it is not normally necessary to operate butone section of the live steam heater. Normally, therefore, the valve 84is closed and as the work approaches the delivery end of the machine itis exposed to dry heat only so that it is delivered substantially dryover the pulley 32.

Upon delivery of the material, it is received by vibratory screen 97which, by way of example, may be supported on rubber mounts 99 andcaused to vibrate in any manner, as, for example, by an unbalanced motor100 supported on an arm 102 projecting from the screen as shown inFIG. 1. The purpose of this screen is to separate from each other any ofthe prefoamed particles of material which may tend to be adherent.However, adhesions are minimized by the fact that the particles aredelivered dry and have never been unduly moistened.

As the separated particles fall through the screen 97, they are guidedby a hopper 104 into a convection delivery pipe 106 into which air isbeing drawn through its suction end 108 to serve as a convection fluidfor propelling the material to a point of storage or use.

The device shown in FIGS. 8 to 10 is essentially like that abovedescribed, differing primarily in the fact that the raw particulatepellets of foamable material are distributed over the surface of thebelt 24 by means of a drum 110 which is mounted for rotation as shown inFIG. 9 and has a screen cloth periphery 112 provided with oblique orhelical fiights 114 which tend to feed the material across the drum fromthe hopper 116 through which the material is admitted to the drum nearone of its ends. Any clumped pellets arriving through the hopper 116will be broken up by the rotation of the drum. The flights 114 will feedmaterial axially of the drum until it falls through the screen cloth 112onto the belt 24 and it has been found that this device will achieve aneffective distribution of the particulate material with considerableuniformity across the area of the belt (as does the shaker 18 and chute22 shown in FIG. 1).

No claim is made to the prefoaming of expandable material by subjectingit to heat on a screen cloth belt. The particular belt used, whilebelieved to be new, is not being claimed herein. The particular featuresas to which the claims are directed include the exposure of particulatefoamable material, preferably distributed in a layer of single particlethickness, to a combination of wet and dry heat provided by live steamand radiant heaters to maintain a precisely controlled temperature at acritical value which achieves the desired expansion of the material inminimum time and delivers it substantially dry and without substantialadhesions, in readiness for immediate use in molding, or for storage ifimmediate use is not desired. As explained above, the live steam desiredto initiate foaming can be used in each of the successive treatmentzones if desired. Even if used in both zones, it will not unduly moistenthe Work particles because of the drying effect of the radiant heat towhich such particles are exposed at temperatures far above 212 F.,preferably throughout their travel through the successive treatmentzones. In actual operation, the use of live steam is preferably limitedto the first zone, where it acts along with the dry heat. For theremainder of the path of travel of the work, it is exposed to dry heatonly.

It may be noted that the progressively increasing cross section of thehood 60 has also been found to be a significant improvement. With a hoodwhich closely confines the material throughout its path of travel, themoisture condensed from the steam remains in intimate contact with thework and the work is not permitted to dry. The combination of the dryheat beneath the belt and the progressively increasing cross section ofthe hood results in the vapor being lifted free of the work anddischarged through the vent pipe 76, thus leaving the work exposed onlyto dry heat for the remainder of its travel through the hood.

We claim:

1. A prefoaming method for the expanding of particulate foamablematerial, such method including the steps of exposing the work particlesto live steam in an enclosure substantially at atmospheric pressure, andpreventing condensation by heating the steam and the work in saidenclosure to a temperature materially in excess of 212 F.

2. A method according to claim 1 in which the work is advanced through asuccession of treatment zones and is subjected to both live steam andradiant heat in at least one of said zones and to radiant heat in theabsence of added steam in a successive zone, the

51 6 live steam and the radiant heat together providing the ReferencesCited ii iil i riifie i i iiiiv ffi fil $53 53535121 322 3: UNITEDSTATES PATENTS substafifiany dry. g 2,704,040 3/1955 Warrington 342l6 XR3. A method according to claim 2 in Which the par- 5 3147321 9/1964Oswald, at 34fi216 XR ticulate material to be prefoamed is exposed tothe 3224452 12/1965 Frankhn et steam and to the dry heat insubstantially a single thick 3,263,981 8/1966 LOWTY- KENNETH w. SPRAGUE,Primary Examiner.

